Cathodically depositable paint binders based on the reaction products of Mannich-bases and epoxy resins are disclosed in many references. Thus, according to DE-OSS Nos. 20 33 770; 23 20 301; 23 57 045; 24 19 179; 25 41 801; 25 54 080; 27 11 385, and 30 45 251, Mannich-bases obtained from polyvalent phenols, secondary amines, and formaldehyde are reacted with epoxy resins, the phenols as well as the epoxy resins being subject to a variety of modifications, for example with semi-blocked diisocyanates, other phenols, or metal salts. As disclosed in the aforementioned references, binders of this type require stoving temperatures of around 190.degree. C. for crosslinking, which nevertheless leads to films having salt spray resistance which is too low for most practical applications. Furthermore, the products crosslink through a splitting off of formaldehyde and amines, causing pollution problems. A substantial part of the development and improvement efforts set forth in the noted patents are, therefore, not directed to enhancing the film properties, but rather are directed to efforts to reduce the polution problem due to the splitting off of substances harmful to the environment. As disclosed in DE-OS No. 25 54 080, for example, in the case of a modification with semi-blocked diisocyanates, the isocyanate groups contribute very little from the standpoint of improving the films but serve primarily to tie up the amines set free on stoving.
PCT Publication No. WO 83/00872 discloses cathodically depositable electrodeposition paint binders which are obtained through co-condensation of partially reacted epoxy resins and phenol resols, and simultaneous or subsequent reaction of the epoxy groups with primary or secondary amines. An essential disadvantage in the manufacture of such products is the necessity of preparing the phenol resols, which, as is known, requires considerable time and produces relatively large quantities of waste water containing phenol and salts. Remnants of salts remaining in the resin may, furthermore, lead to problems on electrodeposition.